For example, in a power conversion device such as an inverter that converts, into an AD, a DC output obtained by power generation by a solar battery, a HERIC CIRCUIT obtained by combining a full-bridge inverter with a switching element that short-circuits is used (for example, refer to Patent Document 1).
As a switching element used in a device such as a power conversion device, an SJ-MOSFET (Super Junction Metal-Oxide-Semiconductor Field effect transistor) having a super junction structure is attracting attention.
FIG. 1A and FIG. 1B each are a schematic sectional view schematically illustrating an internal structure of a MOSFET. FIG. 1A is an SJ-MOSFET having a super junction structure, and FIG. 1B is conventional MOSFET for comparison. The SJ-MOSFET is a MOSFET having a periodic p-n column structure called a super junction structure in a drift layer. While the conventional MOSFET has a depletion layer vertically extending from a p base bottom into a low concentration n layer (drift layer) in an OFF state, the super junction structure has a depletion layer horizontally extending from a vertically extending p-n junction.
In the SJ-MOSFET thus formed, even when the concentration of an n layer that is a current path is increased, depletion is likely to occur. Therefore, the SJ-MOSFET has a characteristic that while high withstand voltage in an OFF state is ensured, on-resistance can be lowered to 1/100 or less of on-resistance in the conventional MOSFET. After the SJ-MOSFET is publicly presented in 1997, active development is performed. For example, horizontal microfabrication of a super junction structure is improved by technological progress of crystal growth, machining technology and the like, so that an aspect ratio can be increased, and on-resistance per unit area is further reduced.